Ultrasound Biometry of Nigerian Fetuses: 2. Femur Length

Abstract

Femur length studies are few in Nigeria and the population used for the studies have been too small to provide a meaningful statistically significant data for the relationship between it and gestational age. Femur length is a very useful parameter for gestational age assessment in the third trimester and therefore requires to be properly studied. Charts of fetal size are widely used in the follow-up of pregnant women, yet no charts have been constructed for the Nigerian population. This study was designed to construct a size chart for femur length in Nigerian fetuses using a large sample size which is evenly distributed from 12 to 42 weeks of pregnancy. A total of 13,740 pregnant women were scanned in a cross-sectional study at the Centre for Reproductive Health Research, Jos over a period of five years. The mean fetal femur length measurements of 13,740 fetuses from 12 to 42 weeks are presented here in a tabulated form together with the regression equation. Mathematical modeling of data demonstrated that the best-fitted regression model to describe the relationship between femur length and gestational age was the second order polynomial regression equation y = – 0.017x2 + 3.2794x – 25.282 with a correlation of determination R2 = 0.999 (p < 0.001) where y is the femur length in millimeters and x is the gestational age in weeks. The mean weekly increase in the femur length in the 4th month of life was 2.6 mm/week, in the 6th month; it was 2.48 mm/week and 2.1 mm/week in the 9th week. A comparison of our chart with others showed significant difference. This chart can be used to provide assessment of gestational age in this country without reliance on Caucasian data as we had done in the past.